1. Field of the Invention:
This invention relates to internal combustion engine parts made of ceramic and metal and having excellent heat insulation, heat resistance and durability, and a method of producing the same.
2. Description of the Prior Art:
Since ceramic materials have excellent mechanical strengths, heat resistance, oxidation resistance and heat insulation, when that portion of an internal combustion engine which contacts with a high temperature combustion gas, such as a piston, a cylinder liner, a cylinder head or the like is composed of a ceramic material, it is possible to raise the combustion temperature and to reduce the heat loss, whereby an improvement of engine efficiency, reduction of harmful components in exhaust gas and the like can be expected. Further, when that portion of the engine which is subjected to repetitive shock loading, such as a tappet, a rocker arm pad or the like is composed of a ceramic material, the wear resistance is improved effectively. Therefore, there are proposed composite engine parts each composed of a combination of metal and ceramic.
For instance, pistons for an internal combustion engine produced by fixing a ceramic piston cap to a top of a metallic piston body through casting are disclosed in Japanese Patent laid open No. 58-95,674 and U.S. Pat. No. 4,245,611. In order to fix the ceramic piston cap to the metallic piston body by casting, however, it is necessary to mitigate the casting stress based on the difference in thermal expansion between the ceramic piston cap and the metallic piston body. For this purpose, there is proposed a method of mitigating the casting stress with a metallic ring provided on the ceramic piston cap (Japanese Patent laid open No. 58-95,674). In this method, however, it is required to form a flange portion for mounting the metallic ring onto the ceramic piston cap, so that not only the shape of the ceramic piston cap becomes complicated but also cracks are apt to occur in the corner portion of the flange due to the stress concentration.
Also, there is proposed a method wherein a cushion layer composed of fibrous ceramic material is interposed between the ceramic piston cap and the metallic piston body to mitigate the casting stress (U.S. Pat. No. 4,245,611). In this method, however, the fixing of the ceramic piston cap to the metallic piston body is insufficient due to the presence of the cushion layer, resulting in the loosening of the piston cap during the use of the piston.
Furthermore, when the ceramic piston cap is fixed to the metallic piston body by casting, it is necessary to preheat the piston cap for preventing the breaking of the piston cap due to the thermal shock produced by the pouring of molten metal, so that the casting operation becomes complicated.
In order to solve the above drawbacks accompanied with the casting, there is proposed a method wherein a metallic member is secured to the ceramic piston cap and then its outer peripheral portion is worked so as to be fixed to the metallic piston body by a mechanical bonding process such as shrink-fitting, screwing or the like. In this method, however, the ceramic piston cap may be broken by contacting with a working tool during the working on the outer peripheral portion of the metallic member.